It has been established that alkylpyrazines are natural components of tobacco smoke, and that they most probably are important contributors to tobacco smoke flavor [A. Baggett et al; J. Chromatog. 97, 79 (1974)]. Further, it has been disclosed in the patent literature that addition of alkylpyrazines to tobacco results in an improvement in the flavor of smoking compositions as judged by an expert panel under subjective test conditions.
U.S. Pat. No. 3,402,051 describes a process for imparting a popcorn-like flavor and aroma to tobacco and foodstuffs by the incorporation of a 2-acetylpyrazine derivative therein.
Other patents which disclose the addition of various pyrazine compounds to tobacco and foodstuffs as a means of providing flavor or flavor enhancement include U.S. Pat. Nos. 3,684,809; 3,705,158; 3,754,934; 3,764,349; 3,767,426; and 3,881,025.
U.S. Pat. No. 3,914,227 discloses pyridyl and pyrazyl ketones and their use in altering the organoleptic properties of tobacco and foodstuffs, and U.S. Pat. No. 4,166,869 discloses acylpyrimidines useful as flavorants for the same type of applications.
Alkylpyridines have also been found to be useful tobacco additives. As an example, U.S. Pat. No. 3,625,224 describes the use of methylpyridines, ethylpyridines and various dialkylpyridines as tobacco additives. U.S. Pat. No. 3,381,691 discloses 2-methyl-5-isopropylpyridine as a tobacco additive.
It is characteristic of pyridine, pyrazine, pyrimidine and other heterocyclic derivatives employed as tobacco flavorants in the prior art, as illustrated by the above described technical literature, that the respective heterocyclic derivatives have the disadvantage of both high volatility and low odor threshold. Both of these properties significantly restrict the extent that these heterocyclic derivatives can be utilized as flavorants in tobacco compositions. A quantity of a pyrazine or pyridine derivative in a tobacco composition sufficient to have a noticeable effect in low delivery cigarettes causes a marked pack aroma.
U.S. Pat. No. 4,259,969 endeavors to overcome some of the disadvantages of the above recited flavorant technology. The said patent describes smoking composition flavorant-release additives such as 2,3-dihydroxy-2,3-dimethyl-1,4-bis(3,5,6-trimethyl-2-pyrazinyl)butane. Under smoking conditions there are released substituted-pyrazine pyrolysis products which enhance the flavor of the mainstream smoke and improve the aroma of the sidestream smoke.
There is continuing research effort to develop improved smoking compositions which contain a new and efficient low volatility flavorant additive, and which generate mainstream smoke with flavorant-enhanced taste and character under smoking conditions.
Accordingly, it is an object of this invention to provide smoking compositions having incorporated therein a flavorant component which is characterized by lack of mobility and/or volatility at ambient temperature.
It is another object of this invention to provide smoking compositions having incorporated therein an additive which under normal smoking conditions contributes improved flavor to mainstream smoke and improved aroma to sidestream smoke.
It is a further object of this invention to provide a novel class of unsymmetrical 2,5-diacylpyrazine compounds.
Other objects and advantages of the present invention shall become apparent from the following description and examples.
Other literature of background interest with respect to the present invention are U.S. Pat. No. 3,452,014 and U.S. Pat. No. 4,064,124 which describe the synthesis of 2,5-disubstituted and 2,3,5,6-tetrasubstituted pyrazines which have utility as starting materials for the manufacture of dyes, fungicides and pharmaceuticals.